Lagrange multi.

We have started to do Lagrange Multi. in my class and my book has a very short section on how to solve these. I was wondering if someone couls help.
The problem is f(x,y)=x^2-y^2 with the constraint x^2+y^2=1.
I have found the partial derv. but I am not sure on what else to do. Any help would be sweet, later.

If you have a function f(x,y), and a constraint g(x,y) = 0, then to find the constrained extrema you set the partial derivatives of f + &lambda;g to zero, and solve for x and y. Remember to take partial derivatives not only with respect to x and y, but also with respect to &lambda;; otherwise, you won't impose the constraint.